Cardiac memory in humans: vectocardiographic quantification in cardiac resynchronization therapy

Abstract

"Cardiac memory" (CM) refers to a change in repolarization induced by an altered pathway of activation. The effects of biventricular pacing on CM induction have not been investigated. To investigate the development of CM during cardiac resynchronization therapy (CRT) through vectorcardiography (VCG). Eleven patients undergoing CRT were enrolled. VCG was acquired during spontaneous ventricular activation at baseline and during AAI and DDD pacing immediately after and 7, 14, 21 and 60days after the implantation. At 1-week follow-up, during AAI pacing T vector angles significantly changed (azimuth 23±19°; p=0.002; elevation 23±27°; p=0.019) and magnitude significantly increased (baseline 1.13±0.69mV; 7days: 1.77±1.27mV; p=0.026). T angle changes remained stable throughout the follow-up period while a further significant increase in magnitude was observed at 60days (2.21±1.50mV; p=0.01 vs. baseline and p=0.04 vs. 7days). Paced T vector magnitude at implant (2.24±1.25mV) decreased significantly at 7days (1.64±1.26mV; p=0.030) with a further significant decrease at 60days (1.40±1.18mV; p=0.003 vs. baseline; p=0.02 vs. 7days). CRT induces a significant change in T vector magnitude, azimuth, and elevation after resumption of spontaneous ventricular activation after 7days from implantation. While further changes in T vector angle were not observed, after 2months of CRT a significant decrease of paced T vector magnitude and a significant increase of spontaneous T vector magnitude were observed.